The present invention relates to a hydraulic control apparatus for a transmission.
There exists a hydraulic control apparatus for a transmission that is mounted in a vehicle or the like. The hydraulic control apparatus is structured such that a line pressure is switched between ranges in two states: (1) a state in which the line pressure is set to a low pressure range (below, simply referred to as a “low pressure state”) and (2) a state in which the line pressure is set to a high pressure range (below, simply referred to as a “high pressure state”) (refer to Japanese Patent Application Publication No. JP-A-2005-133856). This hydraulic control apparatus generally carries out shifting by hydraulically controlling the hydraulic servos of friction engaging elements (a first brake and a second brake) in a transmission that is used in what is termed a “dual-motor power-split hybrid vehicle” and that is interposed between a second motor that outputs a drive force and an output shaft to carry out low/high two stage shifting.
In this hydraulic control apparatus, the valve that regulates and outputs a line pressure urges a spool in one direction when a signal pressure is input from a solenoid valve, and oil pressure from the oil pumps substantially continues to be output from an output port, that is, the line pressure is set to a high pressure state. In addition, alternatively, when a signal pressure is not input from a solenoid valve, based on the urging force of a spring, the spool is controlled so as to attain a position that communicates an input port and a port that is connected to the drawing side of oil pumps (and the port that connects to the lubricating oil duct or the like), and a portion of the oil pressure from the oil pumps is output from the output port, that is, the line pressure is set to a low pressure state. When this line pressure is in the low pressure state, because the oil pump has reduced a portion of the oil pressure, it is possible to implement a reduction in the drive loss of the oil pump, and an improvement in the fuel economy for the vehicle can be attained.